It looks like a wheeze at first, a publicist's gamble to get people to pay twice for the same evening. Yet the double casting of Kristin Scott Thomas and Lia Williams, alternating the roles of wife and interloping stranger, pays dividends in one of Pinter's most mysterious plays. It's worth seeing both versions of 'Old Times', not because doing so clears up the enigma: rather the reverse, it teases out extra possibilities and questions. It also shows two actresses at their peak. Who would have known that Kristin Scott Thomas had so much comedy in her? Who has seen Lia Williams so tart?

Ian Rickson's production is exquisitely pointed. 'Old Times', in which a game of power and possession is played out between a married couple and the wife's former flatmate, shimmers with uncertainty: "I remember things that may never have happened but as I recall them so they take place." That shimmer is there from the beginning, in Peter Mumford's silvery lighting, and in Hildegard Bechtler's design, in which a white sea is glimpsed through gauze curtains. Precision – the opposite of shimmer – is there too, in dialogue that affectionately summons a rackety London life of literary cafes and pubs with men looking up girls' skirts, and the Albert Hall and rain and girls in a bedsit. A wonderful sequence in which husband and friend swap lines from romantic songs – Smoke Gets in Your Eyes, They Can't Take That Away from Me – excavates the heart of that London while also revealing their own passion and fierce rivalry.

I wish I'd seen Pinter, who once played the role, simmering into rage and pain as the husband. Caught between the two women, Rufus Sewell adopts a nervy brightness which makes sense but which doesn't collapse quite convincingly. He is the unchanging factor, yet the shift of parts between the women puts him in a subtly different play. With Scott Thomas as the wife – catlike, contained – and Williams as the temptress visitor, the women are closer together, sometimes looking almost as if they could be two aspects of one person (Visconti much offended Pinter by staging it as a play about a lesbian relationship). This is the subtler version, but not the more arresting.

It's when Williams is the wife – clenched, resentful, quick-tongued, brimming with secret power – and Scott Thomas her ambiguous friend that the play becomes truly arresting. While Williams has a face as closed as a nut, Scott Thomas reveals herself as a natural Pinter seductress. She blazes: when she stretches back on a bed, Sewell hovers over her as if magnetised. She slinks as she rolls up a sleeve or smooths her shirtwaister over her thighs. She seizes on the humour and makes it dance. Is there a flaw in this dazzling double bill? I have only one quibble: that it's a dull stereotype that gives the wife a dull, dark bob and the humdinger a bad blond wig.